In the manufacture of paper products, such as facial tissue, bath tissue, paper towels, dinner napkins and the like, a wide variety of product properties are imparted to the final product through the use of chemical additives. Examples of such additives include softeners, debonders, wet strength agents, dry strength agents, sizing agents, opacifiers and the like. In many instances, more than one chemical additive is added to the product at some point in the manufacturing process. Unfortunately, there are instances where certain chemical additives may not be compatible with each other or may be detrimental to the efficiency of the papermaking process, such as can be the case with the effect of wet end chemicals on the downstream efficiency of creping adhesives. Another limitation, which is associated with wet end chemical addition, is the limited availability of adequate bonding sites on the papermaking fibers to which the chemicals can attach themselves. Under such circumstances, more than one chemical functionality compete for the limited available bonding sites, oftentimes resulting in the insufficient retention of one or both chemicals on the fibers.
Therefore, there is a need for a means of applying more than one chemical functionality to a paper web which mitigates the limitations created by limited number of bonding sites.
In certain instances, two or more chemical functionalities can be combined into a single molecule, such that the combined molecule imparts at least two distinct product properties to the final paper product that heretofore have been imparted through the use of two or more different molecules. More specifically, modified polysaccharides (such as starches, gums, chitosans, celluloses, alginates, sugars, etc.), which are commonly used in the paper industry as strengthening agents, surface sizes, coating binders, emulsifiers and adhesives, can be combined into a single molecule with modified aliphatic hydrocarbons, which are commonly utilized, in conjunction with cationic moieties, as softeners, debonders, lubricants and sizing agents. The resulting molecule is a modified polysaccharide having an aliphatic moiety which can provide several potential benefits, depending on the specific combination employed, including: (a) strength aids that do not impart stiffness; (b) softeners that do not reduce strength; (c) wet strength with improved wet/dry strength ratio; (d) debonders with reduced linting and sloughing; (e) strength aids with controlled absorbency; and (f) surface sizing agents with improved tactile properties.
Hence in one aspect, the invention resides in a modified polysaccharide containing one or more aliphatic hydrocarbon moieties, said modified polysaccharide having the following structure:
Polysacxe2x80x94Z3R1
or
xe2x80x94Polysacxe2x80x94Z3R1xe2x80x94Polysacxe2x80x94
where
Polysac=any polysaccharide, monosaccharide, or sugar residue, modified or unmodified.
R1=any organofunctional group with the only limitation being that R1 must contain a moiety consisting of a saturated or unsaturated, substituted or unsubstituted, linear or branched C8 or higher aliphatic hydrocarbon.
Z3=a bridging radical whose purpose is to attach the R1 functional moiety to the Polysac residue. Suitable bridging radicals would include but are not limited to xe2x80x94OOCxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94NHCOxe2x80x94, xe2x80x94OCNHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, CONHCO, xe2x80x94NCOO, xe2x80x94OSO2Oxe2x80x94, xe2x80x94OCOOxe2x80x94, xe2x80x94OOCxe2x80x94Arxe2x80x94Oxe2x80x94.
In another aspect, the invention resides in a paper sheet, such as a tissue sheet, comprising a modified polysaccharide containing one or more aliphatic hydrocarbon moieties, said modified polysaccharide having the following structure:
Polysacxe2x80x94Z3R1
or
xe2x80x94Polysacxe2x80x94Z3R1xe2x80x94Polysacxe2x80x94
where
Polysac=any polysaccharide, monosaccharide, or sugar residue, modified or unmodified.
R1=any organofunctional group with the only limitation being that R1 must contain a moiety consisting of a saturated or unsaturated, substituted or unsubstituted, linear or branched C8 or higher aliphatic hydrocarbon.
Z3=a bridging radical whose purpose is to attach the R1 functional moiety to the Polysac residue. Suitable bridging radicals would include but are not limited to xe2x80x94OOCxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94NHCOxe2x80x94, xe2x80x94OCNHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, CONHCO, xe2x80x94NCOOxe2x80x94, xe2x80x94OSO2Oxe2x80x94, xe2x80x94OCOOxe2x80x94, xe2x80x94OOCxe2x80x94Arxe2x80x94Oxe2x80x94.
In another aspect, the invention resides in a method of making a paper sheet, such as a tissue sheet, comprising the steps of: (a) forming an aqueous suspension of papermaking fibers; (b) depositing the aqueous suspension of papermaking fibers onto a forming fabric to form a web; and (c) dewatering and drying the web to form a paper sheet, wherein a modified polysaccharide is added to the aqueous suspension or to the web during or after drying, said modified polysaccharide having the following structure:
Polysacxe2x80x94Z3R1
or
xe2x80x94Polysacxe2x80x94Z3R1xe2x80x94Polysacxe2x80x94
where
Polysac=any polysaccharide, monosaccharide, or sugar residue, modified or unmodified.
R1=any organofunctional group with the only limitation being that R1 must contain a moiety consisting of a saturated or unsaturated, substituted or unsubstituted, linear or branched C8 or higher aliphatic hydrocarbon.
Z3=a bridging radical whose purpose is to attach the R1 functional moiety to the Polysac residue. Suitable bridging radicals would include but are not limited to xe2x80x94OOCxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94NHCOxe2x80x94, xe2x80x94OCNHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, CONHCO, xe2x80x94NCOO, xe2x80x94OSO2Oxe2x80x94, xe2x80x94OCOOxe2x80x94, xe2x80x94OOCxe2x80x94Arxe2x80x94Oxe2x80x94.
The amount of the modified polysaccharide added to the fibers can be from about 0.02 to about 2 weight percent, on a dry fiber basis, more specifically from about 0.05 to about 1 weight percent and still more specifically from about 0.1 to about 0.75 weight percent. The modified polysaccharide can be added to the fibers at any point in the process where the fibers are suspended in water.
As used herein, xe2x80x9cpolysaccharidesxe2x80x9d are carbohydrates that can be hydrolyzed to many monosaccharides and include, but are not limited to, starches (primarily starches from potato, corn, waxy maize, tapioca and wheat) which can be unmodified, acid modified, enzyme modified, cationic, anionic or amphoteric; carboxymethylcellulose, modified or unmodified; natural gums, modified or unmodified (such as from locust bean and guar); sugars, modified or unmodified; chitosan, modified or unmodified; and dextrins, modified and unmodified.
A xe2x80x9cmonosaccharidexe2x80x9d is a carbohydrate that cannot be hydrolyzed into simpler compounds.
xe2x80x9cCarbohydratesxe2x80x9d are polyhydroxy aldehydes, polyhydroxy ketones or compounds that can be hydrolyzed to them.
As used herein, xe2x80x9caliphatic hydrocarbonsxe2x80x9d encompasses a broad group of organic compounds, including in general alkanes, alkenes, alkynes and cyclic aliphatic classifications. The aliphatic hydrocarbons can be linear or branched, saturated or unsaturated, substituted or non-substituted.
Methods of making paper products which can benefit from the various aspects of this invention are well known to those skilled in the papermaking art. Exemplary patents include U.S. Pat. No. 5,785,813 issued Jul. 28, 1998 to Smith et al. entitled xe2x80x9cMethod of Treating a Papermaking Furnish For Making Soft Tissuexe2x80x9d; U.S. Pat. No. 5,772,845 issued Jun. 30, 1998 to Farrington, Jr. et al. entitled xe2x80x9cSoft Tissuexe2x80x9d; U.S. Pat. No. 5,746,887 issued May 5, 1998 to Wendt et al. entitled xe2x80x9cMethod of Making Soft Tissue Productsxe2x80x9d; and U.S. Pat. No. 5,591,306 issued Jan. 7, 1997 to Kaun entitled xe2x80x9cMethod For Making Soft Tissue Using Cationic Siliconesxe2x80x9d, all of which are hereby incorporated by reference.